1. Field of the Invention
The present invention relates to internal combustion engines and, more particularly, to internal combustion engines of compact design having high thermal efficiency, very high power-to-weight ratio, high fuel economy, low pollutant emissions, constant horsepower capability, variable compression ratios and variable compression braking.
2. Prior Art
The predominant internal combustion engine configuration presently used is the crankshaft/cylinder arrangement with a working piston reciprocates within a cylinder to drive a rotatable crankshaft. Variations of this configuration have included the in-line, V, radial, and horizontally opposed cylinder alignments. Regardless of the configuration, the piston reciprocates within its cylinder in accordance with one of two predominant operating cycles, namely, the two- or four-stroke spark-ignition Otto cycle or the two- or four-stroke compression-ignition Diesel cycle. With the spark-ignition cycle, a homogeneous mixture of air and fuel at a preferred air/fuel ratio is compressed with ignition caused by an electrical spark or the equivalent. In the compression-ignition cycle, fuel is injected into air that has been compressed to cause an adiabatic increase in its temperature to a temperature above the auto- or self-ignition temperature of the fuel.
Both types of operating cycles and the various physical engine configurations that have been developed have proved satisfactory although each has attendant drawbacks.
In the spark-ignition engine, the fuel must be premixed with air to provide a desirably homogeneous mixture with the ratio of the air to the fuel controlled so as to fall within a preferred ratio range, e.g., between 11:1 and 17:1. Air/fuel ratios greater than 17:1 result in mixtures which may or may not combust and air/fuel ratios below 11:1 result in mixtures which are inefficient from the standpoint of fuel consumption and unacceptable with regard to pollution. Additionally, the compression ratio of the spark ignition engine is limited to some maximum so as not to cause unintentional pre-ignition of the homogeneous air/fuel mixture during the compression stroke. The compression ratio limit also disadvantageously limits the thermal efficiency of spark-ignition engines.
In contrast to the spark-ignition engine, the compression-ignition engine utilizes air that has been heated during the compression stroke to a temperature greater than the auto-ignition temperature of the fuel so that fuel can be injected in a heterogeneous manner into the so-heated air to cause burning. Thus, the fuel injected in a compression-ignition engine can be burned in considerable excess air to provide a rather large mass of heated air for the expansion stroke, but does not use all the available air in the cylinder for combustion. Accordingly, the compression-ignition engine provides a substantial increase in thermal efficiency compared to the spark-ignition engine. Unfortunately, compression-ignition engines require a rather sophisticated and expensive fuel delivery and injection system that mitigates against the increase in thermal efficiency.
In the traditional crankshaft/cylinder arrangement, regardless of the particular operating cycle implemented, the piston is usually at or near its uppermost position (TDC) during that portion of the cycle in which the fuel is ignited. In this configuration, the crankshaft throw position presents a moment arm against which the piston acts that is the smallest of the operating cycle, and, accordingly, the mechanical conversion efficiency of the combustion products expanding against the piston during that portion of the cycle is poor.
Additionally, the mechanical constraints of the traditional crankshaft/connecting rod arrangement is such that it is very difficult to vary the compression ratio of the engine, since the crankshaft throw distance and the connecting rod length are fixed and not easily changed. Because of this, the traditional crankshaft/connecting rod arrangement is not amenable to variable compression schemes. As can be appreciated, a variable compression engine would permit the use of various types and grades of fuels and is particularly suitable in situations where the cost of various alternative engine fuels varies or where fuel supplies may be uncertain, such as in a military environment. In addition to the mechanical constraints of the crankshaft/connecting rod arrangement, the traditional cam operated valve train necessitates a fixed valve timing that is optimum for only a portion of the engine power curve. As can be appreciated, variable valve timing would permit optimization over the entire engine operating range.